TO READ IN BOOK FORMAT, OR TO PRINT THIS ARTICLE: What is Natural Law
Definition. Natural law is simply a remnant of the knowledge of God’s will with which man was created.
Background. Man was created with a perfect knowledge of a moral will which the Creator had given to man to govern him. That is, man had a perfect understanding of God’s moral will. Simply put: This moral law was the knowledge of right and wrong. All souls that would be born into this world will have this same moral law “written into their hearts” (Romans 2:5), as Scripture puts it.
Indeed, after the Fall into sin, the descendents of our first ancestors were born with this moral law in their minds. However, on account of the presence of inherited sin which was also in these same minds, the knowledge of this moral law was no longer perfect. To be sure, it had not been erased, but it was obscured or blurred. Out of his mercy God gave sinful man the Ten Commandments. Then he elaborated further on these commandments throughout the Bible.
Hence natural law will have to be consistence with God’s biblically revealed moral law. This moral law is the standard which natural law must follow. God’s moral law is the clearer of the two.
Furthermore, not only is the moral law of God transmitted to every soul which is conceived, but every soul also receives from God a conscience. In practice the conscience will act like a judge. It will look at the moral law written in the heart, and then it either will condemn or approve of each moral act committed.
In Romans 2:14 the holy writer speaks of heathen people who had no knowledge of the Ten Commandments, but only of that moral knowledge which “was written in their hearts.” He declares that though they had no knowledge of the Ten Commandments, at times they still would “do by nature the things contained in the” Ten Commandments. That is to say, they still would follow this natural law. Furthermore, in doing so they would demonstrate that there is a moral law of God “written in their hearts.”
Thus only the Bible could define natural law accurately, properly, and with divine assurance. Men who would define natural law without the revelation of the Bible, at best could do it partly and without divine assurance.
Indeed, unregenerate men in their spiritual blindness reject the Ten Commandments and attempt to codify natural law based on their biased preconceptions instead. As a result of this deliberately-biased process being forced through their intellect, such ideas as “the social contract,” “the consent of the governed,” and “the right to revolution” have been promoted, all of which contradict God’s moral law which is revealed in the Bible.
History. “Church fathers, especially Latin, some of whom were deeply influenced by Roman law, shared this concept of natural law but identified it with the primitive natural revelation of God in man’s heart…. The Protestant Reformation generally accepted the patristic view of natural. Martin Luther… followed Augustine of Hippo in regarding the decalog as the directly revealed codification of natural law. But the Renaissance, especially in its humanistic aspects, deemphasized the divine and overemphasized the purely rational character of natural law. As a result, in the age of reason… the concept of natural law was pressed into service as the ideological basis of ‘natural rights’, the ‘social contract’…constitutional government based on the consent of the governed, and the right of revolution. In one form or another this is the view of R. Hobbes, J. Locke, T. Jefferson… T. Paine and J. J. Rousseau. The most typical and political effective expressions of this view are the American Declaration of independence and the French Declaration of the Rights of Man and of the Citizen.”
Jus naturale. “The natural law….This concept originated with the philosophical jurists of Rome, and was gradually extended until the phrase came to denote a supposed basis or substratum common to all systems of positive law, and hence to be found, in greater or less purity, in the laws of all nations. And, conversely, they held that if any rule or principle of law was observed in common by all peoples with whose systems they were acquainted, it must be a part of the jus naturale, or derived from it. Thus the phrases ‘jus naturale’ and ‘jus gentium’ came to be used interchangeably.”
Jus gentium. “The law of nations. That law which natural reason has established among all men is equally observed among all nations, and is called the ‘law of nations’, as being the law which all nations use…. It was originally a system of law, or more properly equity, gathered by the early Roman lawyers and magistrates from the common ingredients in the customs of the old Italian tribes, – those being the nations, gentes, whom they had opportunities of observing, – to be used in cases where the jus civile did not apply; that is, in cases between foreigners or between a Roman citizen and a foreigner. The principle upon which they proceeded was that any rule of law which was common to all the nations they knew of must be intrinsically consonant to right reason, and therefore fundamentally valid and just.” 
“This expression, ‘natural law’, or jus naturale, was largely used in the philosophical speculations of the Roman jurists of the Antonine age, and was intended to denote a system or rules and principles for the guidance of human conduct which, independently of enacted law or of the systems peculiar to any one people, might be discovered by the rational intelligence of man, and would be found to grow out of and conform to his nature, meaning by that word his whole mental, moral, and physical constitution. The point of departure for this conception was the Stoic doctrine of a life order ‘according to nature’, which in its turn rested upon the purely supposititious existence, in primitive times, of a ‘state of nature’; that is, a condition of society in which men universally were governed solely by a rational and consistent obedience to the needs, impulses, and promptings of their true nature, such nature being as yet undefaced by dishonesty, falsehood, or indulgence of the baser passions. In ethics, it consists in practical universal judgments which man himself elicits. These express necessary and obligatory rules of human conduct which have been established by the author of human nature as essential to the divine purposes in the universe.”
In light of the history and of these descriptions of natural law by Black’s Law Dictionary, the following is what it defines as moral law. “The law of conscience; the aggregate of those rules and principles of ethics which relate to right and wrong conduct and prescribe the standards to which the actions of men should conform in their dealings with each other.”
Confer also this definition of “imperfect obligation”! “The duty of exercising gratitude, charity, and the other merely moral duties are examples of this kind of obligation.”
Conclusion. While unbiblical men could only imagine what natural law would mean, the Bible authoritatively and assuredly will reveal what it is. Therefore, depend on what the Bible commands is God’s moral law for men! Reject any prideful presumptions of natural law which men would promote which contradict the clear laws of God!
 The Lutheran Cyclopedia, editor Erwin L. Lueker (Saint Louis: Concordia, 1975), page 567f.
 Black’s Law Dictionary, Fifth edition (Saint Paul: West, 1979), page 773B.
 Black’s Law Dictionary, Fifth edition (Saint Paul: West, 1979), page 772A & B.
 Black’s Law Dictionary, Fifth edition (Saint Paul: West, 1979), page 925A & B.
 Black’s Law Dictionary, Fifth edition (Saint Paul: West, 1979), page 909B.
 Black’s Law Dictionary, Fifth edition (Saint Paul: West, 1979), page 969B.
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